(i) Field of the Invention
A certain aspect of the present invention relates to semiconductor devices. Another aspect of the present invention relates to a semiconductor device that has a field plate formed on a silicon nitride film between a gate electrode and a drain electrode.
(ii) Description of the Related Art
By a known technique for semiconductor devices that perform high-voltage operations, a field plate is formed on an insulating film between the gate electrode and the drain electrode (National Publication of International Patent Application No. 2007-537593, for example). The potential of the field plate is set at a predetermined potential (the ground potential, for example), so that the field intensity can be reduced in the vicinity of a region that is located between the gate electrode and the drain electrode and is also located below the field plate. Accordingly, by forming a field plate on a region having a high field intensity, the field intensity between the gate electrode and the drain electrode can be made uniform, and the withstand voltage between the source and the drain or the withstand voltage between the gate and the drain can be made higher. Also, by making the field intensity uniform, current collapses can be restrained. Further, the field plate is formed to cover part of the gate electrode, and is made to have the same potential as that of the source electrode. In this manner, the feedback capacitance between the gate and the drain can be reduced.
As illustrated in FIG. 4 of National Publication of International Patent Application No. 2007-537593, a step portion that reflects the shape of the gate electrode is formed in the insulating film formed to cover the gate electrode, and a field plate is formed along the step portion of the insulating film. In a semiconductor device having such a structure, a failure might occur in a high-temperature, high-voltage operation.